I suggest you use LINQPad as a first start.
Gamlor has a great tutorial on how to use LINQPad with db4o. You'll need to modify that a bit so you use client-server access (thus not locking your db).
I don't want to re-post his code here, because I think it's pointless and he's also a user here, don't wanna win his laurels.
For me, LINQPad seems to be the best approach, also because I can use it on my server, where I'd be having trouble with OME for obvious reasons.
